Fix handling of directory names with special characters

[jul13579]

This PR fixes an issue that prevents the photos app to display media of directories that contain special characters such as the & character. When e.g. adding a media folder that is named Photos & Videos, the request to dav/ errors with Parse error: xmlParseEntityRef: no name on line XX, column YY, resulting in the "all media" view staying empty and a notification appearing in the top left stating "Error fetching files". This PR resolves this issue by encoding media directory names such that embedding them in the XML payload sent to dav/ does not yield invalid XML.

[github-actions]

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